1. Field of the Invention
The present invention relates to an apparatus and a method for receiving digital broadcasting, and more particularly to a digital broadcast receiver for providing an automatic channel switching function of digital broadcasting.
2. Description of the Related Art
A Digital Multimedia Broadcasting (DMB) service is a broadcasting service in which users can watch multimedia broadcastings through multi-channels by means of a personal portable receiver or a vehicle receiver, which has a non-directional receive antenna, even while the users are moving. Specifically, a satellite DMB adopted in Korea corresponds to an International Telecommunication Union (ITU) standard Rec.BO.1130-4: System-E, and employs Code Division Multiplexing (CDM) technology which is similar to a Code Division Multiple Access (CDMA) mobile telephone technology.
Typically, a satellite DMB uses a Motion Picture Experts Group (MPEG)-2 Transport Stream (TS) as a transmission standard. According to such a DMB broadcasting standard, a DMB broadcasting channel includes a pilot channel for transmitting configuration information of a CDM channel having Walsh code information, a Conditional Access System (CAS) channel for transmitting authentication information for DMB broadcasting reception, an Electronic Program Guide (EPG) channel for transmitting information for a service channel, and at least one media channel for actually transmitting TS packet data.
A digital broadcasting center transmits Program Specific Information (PSI) to a digital broadcast receiver, and the digital broadcast receiver may receive TS data according to channels selected by a user with reference to the PSI. The PSI includes a Service Description Table (SDT), a Program Association Table (PAT), and a Program Map Table (PMT). The SDT includes broadcasting service channels currently being provided, and information relating to the broadcasting service channels. A user may select desired channels with reference to the SDT. The PAT includes the Packet Identification (PID) of a PMT having the ID of a broadcasting channel currently being provided and additional information of the broadcasting channel. Last, the PMT includes PIDs of video and audio TSs corresponding to each individual broadcasting channel.
That is, in order to output DMB of a predetermined broadcasting channel, the digital broadcast receiver must know the PID's Packet Elementary Stream Packet Identification (PES PID) of TS packet data of the channel. The PES PID can be understood by detecting the ID of the channel, which has been selected by a user from the SDT, from the PAT and the PMT.
Accordingly, the digital broadcast receiver receives only TS packet data having a PES PID of the channel selected by the user, thereby providing the user with a DMB service for the channel selected by the user. For this, the digital broadcast receiver must filter only the TS packet data, which has the PES PID of the channel selected by the user, from TS packet data broadcasted from a digital broadcasting reception center. A Walsh code is used for the filtering of the TS packet data.
The Walsh code represents a kind of set of orthogonal codes. In an MPEG-2 which is a transmission standard of a terrestrial DMB, the Walsh code is used in order to filter only the TS packet data of a specific channel. Information for the Walsh code is transmitted through the pilot channel of the five channels in the DMB transmission standard as described above. The digital broadcast receiver receives information for a range of a maximum PID value and a range of a minimum PID value for each CDM channel from the pilot channel. Accordingly, when a user selects one channel, the digital broadcast receiver sets a Walsh code value for the corresponding channel in a DMB module, and filters only TS packets having PES PIDs within the maximum/minimum PID range of the set Walsh code for reception.
That is, in order to receive the TS packet data corresponding to the channel selected by the user, the digital broadcast receiver must search for Walsh codes corresponding to PMT PIDs and PES PIDs of the channel selected by the user, and set Walsh codes searched by a baseband processor.
FIG. 1 is a block diagram illustrating the construction of the conventional digital broadcast receiver. The conventional digital broadcast receiver includes a DMB module 10, a TS demultiplexer 20, a codec 30, a speaker 40, and a display unit 50. The DMB module 10 selects and receives a CDM channel corresponding to a broadcasting channel selected by a user, and outputs TS data for a corresponding broadcasting channel.
The TS is illustrated in FIG. 2 which is a diagram illustrating the structure of a conventional transport stream (TS) data output from a digital multimedia broadcasting (DMB) module. The TS 60 output from the DMB module 10 includes a stream type field 61, a channel number field 62, a PID field 63, and an audio PMT PID field 64. The stream type field 61 represents an audio type TYPE_AUDIO or a video type TYPE_VIDEO representing the type of information contained in the TS data stream as will be described below. The channel number field 62 represents a current channel number, and the PID field 63 represents a PID for a current channel. When a current stream is an audio stream, the PID corresponds to an audio service ID. However, when the current stream is a video stream, the PID corresponds to a PMT PID of a corresponding channel. The audio PMT PID field 64 is a valid field only when a stream type is audio, and becomes a PMT PID of a corresponding audio channel. When the stream type is not an audio, the field has a value of 0 i.e., a “0” is sent.
The TS demultiplexer 20 having received the TS data demultiplexes the TS data according to each broadcasting channel, and provides the codec 30 with the demultiplexed data. The codec 30 converts digital signals to voice signals or image signals, and outputs the voice signals and the image signals to the speaker 40 and the display unit 50, respectively.
In the digital broadcast receiver, a user manually and successively inputs a channel switching key and views programs currently being provided on a one-by-one basis, in order to select a desired program from the programs currently being provided. However, it takes about 4-5 seconds to switch from one channel to the next channel. Therefore, because of the lengthy switching times, the user is inconvenienced when switching channels to select a desired broadcast.